#300990 - 29/07/2007 23:48
Long Distance wireless link
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carpal tunnel
Registered: 19/01/2002
Posts: 3584
Loc: Columbus, OH
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Ok, so I'm probably moving to a remote area of Belize within the next few months. The place I'm moving to does have a satellite internet connection powered by solar power, but I'd like to get a lower latency connection out there. Fortunately, we're right on the beach and there's a straight shot over the water to Belize City. In Belize City, we have an apartment with a DSL connection. I'm looking into the possibility of using highly directional antennae to shoot a wireless connection between my location and the apartment in the city. Added difficutly: even though we have line-of-sight, the distance between the two points is about 22.5 miles.
Having read some articles on the internet, it seems conceivable to get a reasonable connection over that distance. Also, since I don't have to worry about the FCC, perhaps boosting the signal strength is an option.
Does anyone have any experience with doing something like this?
Does anyone know the formula to figure out how tall the tower would need to be to account for the earth's curvature?
Does anyone know of a cheapish way to aim the antennae without using an expensive spectrum analyzer?
I'm sure I'll have some more questions as I work through putting this together....thanks in advance.
EDIT, approximate locations for the interested:
Where I'll be living:
17.185106, -88.305032
Apartment in Belize City:
17.490298, -88.186451
Edited by JBjorgen (29/07/2007 23:52)
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~ John
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#300991 - 30/07/2007 02:41
Re: Long Distance wireless link
[Re: JBjorgen]
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carpal tunnel
Registered: 20/12/1999
Posts: 31597
Loc: Seattle, WA
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Quote:
Ok, so I'm probably moving to a remote area of Belize within the next few months.
And I'm so very sad about it. 
You've been such a fantastic web site host for me. I hate to see it go.
Guess it's time to start shopping around again. Ricin, you still hosting these days? 
I wish you the best of luck and success in Belize.
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#300992 - 30/07/2007 05:24
Re: Long Distance wireless link
[Re: JBjorgen]
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carpal tunnel
Registered: 17/01/2002
Posts: 3996
Loc: Manchester UK
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Wow, what are you doing there?
I've set a couple of links up. I ended up using a cheap 2.4GHz video link and firing that over the link. I simply then aimed the dishes while looking at a portable TV, seemed to work really well.
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Cheers,
Andy M
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#300993 - 30/07/2007 06:44
Re: Long Distance wireless link
[Re: andym]
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carpal tunnel
Registered: 24/12/2001
Posts: 5528
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Quote:
I've set a couple of links up. I ended up using a cheap 2.4GHz video link and firing that over the link. I simply then aimed the dishes while looking at a portable TV, seemed to work really well.
Hmm. Thats a pretty neat trick. Aiming the dish is still going to be hard but at least you get a near enough instant indication that you're doing it right.
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#300995 - 30/07/2007 13:02
Re: Long Distance wireless link
[Re: andym]
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carpal tunnel
Registered: 19/01/2002
Posts: 3584
Loc: Columbus, OH
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Quote:
Wow, what are you doing there?
Religious and charity work.
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~ John
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#300996 - 30/07/2007 15:10
Re: Long Distance wireless link
[Re: tman]
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pooh-bah
Registered: 15/01/2002
Posts: 1866
Loc: Austin
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Try a green laser to help aim! Just don't aim it at any planes.
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#300997 - 30/07/2007 15:29
Re: Long Distance wireless link
[Re: RobotCaleb]
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carpal tunnel
Registered: 25/12/2000
Posts: 16706
Loc: Raleigh, NC US
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That was my first thought, too, but I can't imagine that any consumer laser will still be visible over 22.5 miles.
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Bitt Faulk
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#300998 - 30/07/2007 15:49
Re: Long Distance wireless link
[Re: wfaulk]
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pooh-bah
Registered: 15/01/2002
Posts: 1866
Loc: Austin
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And at that distance to keep it steady enough and to adjust it the minute distances need to make changes you'd need some sort of fancy worm-gear thingamabob. At least, that's what it looks like in my head.
Maybe a really wide laser beam would be better. Say, 2 feet wide?
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#301000 - 30/07/2007 16:07
Re: Long Distance wireless link
[Re: RobotCaleb]
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carpal tunnel
Registered: 25/12/2000
Posts: 16706
Loc: Raleigh, NC US
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Holy crap. "Light cigars"?!? With a frickin' laser beam?
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Bitt Faulk
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#301001 - 30/07/2007 16:24
Re: Long Distance wireless link
[Re: RobotCaleb]
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carpal tunnel
Registered: 24/12/2001
Posts: 5528
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Quote:
Try a green laser to help aim! Just don't aim it at any planes.
Getting the laser aligned with your own dish will be an issue still. A tiny fraction of a degree out on your side and what the dish is pointing at and what your laser is pointing at will be totally different.
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#301002 - 30/07/2007 17:02
Re: Long Distance wireless link
[Re: wfaulk]
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pooh-bah
Registered: 06/02/2002
Posts: 1904
Loc: Leeds, UK
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Quote:
Holy crap. "Light cigars"?!? With a frickin' laser beam?
SSSSSHHHHHH!!!!!!!! Don't let Godfrey hear you! He may start smoking them again if he knows you can light them with a laser beam 
Cheers
Cris
PS - After typing this I realised that boxer smoked a pipe not cigars, but you get the idea
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#301003 - 30/07/2007 17:49
Re: Long Distance wireless link
[Re: wfaulk]
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carpal tunnel
Registered: 20/12/1999
Posts: 31597
Loc: Seattle, WA
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Quote:
Holy crap. "Light cigars"?!? With a frickin' laser beam?
There's a shot at the beginning of the Pink Floyd "Delicate Sound of Thunder" concert video of the lighting technician who runs the laser system doing exactly that.
The lasers they use for concerts are definitely that powerful.
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#301004 - 30/07/2007 20:01
Re: Long Distance wireless link
[Re: JBjorgen]
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addict
Registered: 02/04/2002
Posts: 691
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I'd have to climb up on the roof to check my antenna, but on the back of it they're 4 or 5 LEDs which act like a cell phone signal strength indicator. It took about 2 minutes to align my antenna, and I'm getting about 8ms of latency through it. I'm not on the longest run, I'm about 4 miles away, but these same antennas are going about 17 miles I think. They also do hardware channel hopping. I think they use one channel for upstream, another for downstream, and they rotate if any noise/interference is detected. I actually need to weld up a nicer mount, as one of the ice storms this winter caused it to drop from 95% signal strength to about 3%. Maybe I'll do that this week while the weather is still nice. Nothing like climbing around on an icy roof just for internet access
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Oliver
mk1 30gb: 129 | mk2a 30gb: 040104126
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#301005 - 30/07/2007 20:52
Re: Long Distance wireless link
[Re: oliver]
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carpal tunnel
Registered: 19/01/2002
Posts: 3584
Loc: Columbus, OH
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The next logical question is, what antenna are you using?
_________________________
~ John
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#301006 - 30/07/2007 21:44
Re: Long Distance wireless link
[Re: tfabris]
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carpal tunnel
Registered: 13/02/2002
Posts: 3212
Loc: Portland, OR
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Quote:
Quote:
Holy crap. "Light cigars"?!? With a frickin' laser beam?
There's a shot at the beginning of the Pink Floyd "Delicate Sound of Thunder" concert video of the lighting technician who runs the laser system doing exactly that.
The lasers they use for concerts are definitely that powerful.
Well, given that one can cut and weld metal with lasers, I'd think that lighting a bit of flammable weed and paper isn't that much of a stretch. I'm more surprised at the portability, and accessibility, in general, of lasers with that much power.
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#301007 - 30/07/2007 23:47
Re: Long Distance wireless link
[Re: canuckInOR]
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carpal tunnel
Registered: 25/12/2000
Posts: 16706
Loc: Raleigh, NC US
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Well, that's what I meant. Handheld laser powered by a few AA batteries.
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Bitt Faulk
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#301008 - 31/07/2007 12:35
Re: Long Distance wireless link
[Re: JBjorgen]
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pooh-bah
Registered: 13/01/2002
Posts: 1649
Loc: Louisiana, USA
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Hmm, maybe something like this?Stu
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If you want it to break, buy Sony!
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#301009 - 31/07/2007 13:26
Re: Long Distance wireless link
[Re: wfaulk]
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carpal tunnel
Registered: 20/12/1999
Posts: 31597
Loc: Seattle, WA
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Quote:
Well, that's what I meant. Handheld laser powered by a few AA batteries.
Good point. Now that I look closer at the wickedlasers site, it looks like the ones that can light cigars (200-300mw) use Li-ion batteries, but same difference. I wouldn't think you'd be able to get that kind of power out of batteries. That's pretty impressive.
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#301010 - 31/07/2007 13:43
Re: Long Distance wireless link
[Re: tfabris]
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pooh-bah
Registered: 13/01/2002
Posts: 1649
Loc: Louisiana, USA
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You can fashion a similar performing laser by harvesting the diode from a high speed DVD burner.
Stu
_________________________
If you want it to break, buy Sony!
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#301011 - 31/07/2007 15:52
Re: Long Distance wireless link
[Re: maczrool]
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carpal tunnel
Registered: 20/12/1999
Posts: 31597
Loc: Seattle, WA
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No. Seriously. A DVD burner's diode laser can operate at 200mw?
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#301012 - 31/07/2007 15:59
Re: Long Distance wireless link
[Re: tfabris]
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pooh-bah
Registered: 13/01/2002
Posts: 1649
Loc: Louisiana, USA
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Quote:
No. Seriously. A DVD burner's diode laser can operate at 200mw?
See here. I've tried it. It really does work.
Stu
_________________________
If you want it to break, buy Sony!
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#301014 - 01/08/2007 10:04
Re: Long Distance wireless link
[Re: JBjorgen]
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carpal tunnel
Registered: 29/08/2000
Posts: 14493
Loc: Canada
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Quote:
Does anyone know of a cheapish way to aim the antennae without using an expensive spectrum analyzer?
Unlike lasers, radio waves spread out with distance. So ultra-precision isn't strictly necessary here.
A handheld GPS receiver can be used to measure the exact locations of the two antennas, assuming you can get a reasonably clear view of the sky from the city apartment (rooftop directly above the antenna?).
Once you have the GPS positions, that same handheld GPSr can tell you the exact bearing between them, which gives the angle at which they must be aimed to "see" each other.
Or use a telescope... mmm.. that might be the easiest here.
For height to avoid earth curvature, one of the math types here should know. I think 30' should be sufficient, though.
Cheers
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#301015 - 01/08/2007 12:32
Re: Long Distance wireless link
[Re: mlord]
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carpal tunnel
Registered: 25/12/2000
Posts: 16706
Loc: Raleigh, NC US
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Quote:
Unlike lasers, radio waves spread out with distance. So ultra-precision isn't strictly necessary here.
That is not true in my experience. I've aligned a few wireless link antennas in my time and a few millimeters one way or another seems to make a big difference. This probably has far more to do with aligning the receiving dish than it does the transmitting antenna. The very fact that they do spread is probably what makes that alignment critical, as a few degrees off on a parabolic reflector can change the focus signficantly. I would imagine that a distance of about 22 miles would require a parabolic dish, but I could be wrong.
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Bitt Faulk
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#301016 - 01/08/2007 12:46
Re: Long Distance wireless link
[Re: wfaulk]
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carpal tunnel
Registered: 29/08/2000
Posts: 14493
Loc: Canada
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Quote:
Quote:
Unlike lasers, radio waves spread out with distance. So ultra-precision isn't strictly necessary here.
That is not true in my experience. I've aligned a few wireless link antennas in my time and a few millimeters one way or another seems to make a big difference. This probably has far more to do with aligning the receiving dish than it does the transmitting antenna. The very fact that they do spread is probably what makes that alignment critical, as a few degrees off on a parabolic reflector can change the focus signficantly. I would imagine that a distance of about 22 miles would require a parabolic dish, but I could be wrong.
I imagine that a pair of yagi or log antennas would do the trick nicely. And at 22km, the beam spread will be many metres, rather than a pencil (remember those?) eraser tip (laser).
Cheers
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#301017 - 01/08/2007 12:56
Re: Long Distance wireless link
[Re: mlord]
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carpal tunnel
Registered: 24/12/2001
Posts: 5528
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Quote:
pencil (remember those?)
You mean an AMD Athlon multiplier unlocking tool?
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#301018 - 01/08/2007 13:11
Re: Long Distance wireless link
[Re: mlord]
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carpal tunnel
Registered: 25/12/2000
Posts: 16706
Loc: Raleigh, NC US
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Quote:
For height to avoid earth curvature, one of the math types here should know. I think 30' should be sufficient, though.
Ooh. That's a good one.
First, we need to determine the angle of the vertex at the center of the earth to one of the stations and the midpoint (that is, high spot) of the line connecting the two stations. We know the length of all three sides, so we can use the oblique triangle formula: a^2 = b^2 + c^2 - 2bc(cosA). b and c are the radius of the earth (call it r for easier calculations, and assume the maximum radius -- 6379km -- for head room) and a is half of the 22 miles (call it 18km for a little head room, shown as "d" in the picture). Give that b=c=r, the formula reduces to a^2 = 2r^2(1-cosA) and solving for cosA leaves cosA = 1 - (a^2/2r^2). Add in real numbers and you get cosA = 0.999996019... and then A = 0.1616749292 degrees. (Actually, because of the next step, we don't even need to resolve the actual angle.)
Now we need to find the length of the hypotenuse of a right triangle with one angle being A from above and the side adjacent to A being the radius of the earth. We know that cosA = adjacent/hypotenuse. So cosA = r/h. We know A and r, so solve for h: h = r/cosA. Plug in real numbers and you get h = 6379.025396, or 0.025396km longer than the radius of the earth. That's over 25 meters, or over 83 feet. Significant. That's 83 feet on each side. I hope you're living in a tall apartment building.
Edited by wfaulk (01/08/2007 13:25)
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Bitt Faulk
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#301019 - 01/08/2007 13:46
Re: Long Distance wireless link
[Re: wfaulk]
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carpal tunnel
Registered: 19/01/2002
Posts: 3584
Loc: Columbus, OH
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I'll be lucky if I can get 25' on the apartment building side., so that means it'd need to be about 150' on the other side. Hmm...that may be cost prohibitive. We've got a building that's about 40' high and I was hoping to be able to just put a mast on top of it.
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~ John
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